Apparatus for utilizing compatible perforating fluid in well bores

ABSTRACT

A well tool apparatus having a perforating section at its lower end has an upper section comprised of a reservoir containing a compatible perforating fluid and a pump for pumping such fluid down through the perforating section and out the lower end of the tool. Means are provided for causing the perforating fluid to displace the well bore fluid in the region along the length of the perforating section, such displaced fluid being recaptured above a floating piston in the reservoir containing the perforating fluid. In an alternative embodiment, a protective shield is utilized around the perforating tool and means are provided for releasing the perforating fluid into the annulus between the shield and the perforating section, the lower end of the shield having a port for releasing the perforating fluid into the annulus between the instrument and the casing to be perforated.

United States Patent 1 1 [111 3,856,094 Davis 1 Dec. 24, 1974 1APPARATUS FOR UTILIZING COMPATIBLE PERFORATING FLUID IN WELL BORES [75]Inventor: Mike Davis, Houston, Tex. [73] Assignee: Dresser Industries,Inc., Dallas, Tex.

[22] Filed: Nov. 1, 1973 [21] Appl. No.: 411,982

[52] U.S. Cl 175/452, 175/459, 166/162, 166/297 [51] Int. Cl E2lb 43/116[58] Field of Search 175/452, 2, 4.59, 4.6; 166/162, 163, 165, 168, 297

[56] References Cited 7 UNITED STATES PATENTS I 3,011,551 12/1961 Younget al. 175/452 3,115,932 12/1963 Reynolds 175/452 3,138,206 6/1964 Bruceet a1. 175/452 3,433,302 3/1969 Shore 175/452 X 3,463,248 8/1969 Bell175/452 Primary Examiner-David H. Brown Attorney, Agent, or Firm-WilliamE. Johnson, Jr.

[ ABSTRACT A well tool apparatus having a perforating section at itslower end has an upper section comprised of a reservoir containing acompatible perforating fluid and a pump for pumping such fluid downthrough the perforating section and out the lower end of the tool. Meansare provided for causing the perforating fluid to displace the well borefluid in the region along the length of the perforating section, suchdisplaced fluid being recaptured above a floating piston in thereservoir containing the perforating fluid. In an alternativeembodiment, a protective shield is utilized around the perforating tooland means are provided for releasing the perforating fluid into theannulus between the shield and the perforating section, the lower end ofthe shield having a port for releasing the perforating fluid into theannulus between the instrument and the casing to be perforated.

6 Claims, 4 Drawing Figures SURFACE ELECTRONICS APPARATUS FOR UTILIZINGCOMPATIBLE PERFORATING FLUID IN WELL BORES BACKGROUND OF THE INVENTIONThe present invention releates generally to method and apparatus forproducing clean perforations in wells and particularly to method andapparatus for displacing well fluids within a cased borehole in the areato be perforated with fluids which are compatible with perforations.

When an oil well casing is perforated in the presence of well fluidscontaining colloids and other particulate matter for pressure control,the perforation in the oilbearing formation is often sealed with afilter cake. The prior art has recognized that it is desirable todisplace the fluids in the area of the perforation with so-calledcompletion fluids in order to produce clean perfora tions. Typical ofsuch prior art is US. Pat. No. 3,1 38,206 to George H. Bruce et al; U.S.Pat. No. 2,842,205 to Allen et al; and U.S. Pat. No. 2,963,088 toCorley. For example, in the Bruce et al patent, the completion fluid ispumped from a reservoir into the annulus between the perforating sectionand the casing to be perforated. This device attempts to cause thedisplaced well fluid to be pumped down to the open lower end of theperforating section and up through the interior of a packer and out intothe annulus above the packer. However, such a device as is shown in theBruce et al reference is quite complex and expensive to fabricate.Furthermore, in the Bruce et al system, the compatible fluid isintroduced into the annulus above the perforator and is thus dependentupon the displaced fluid being pumpeddown the annulus and then back upthrough the interior of the perforatonThus, the interior of theperforatorhas to be modified to provide a tortuous path around theshaped charges within the gun. It should also be appreciated that theBruce et al apparatus is dependent upon extremely intricate piping tomaintain a separationbetween the well fluids and the compatibleperforating fluid.

It is therefore the primary object of the present invention to provide anew and improved method and apparatus for displacing the well bore fluidin the area of the casing to be perforated with a fluid which iscompatible with such perforations; and

It is another object of the invention to provide a new and improvedmethod and apparatus for displacing well bore fluid with compatibleperforating fluid without necessarily modifying the interior of theperforating gun.

These and other objects of the present invention are accomplished,generally, by a method and apparatus which utilizes a flow passagethrough the interior of a perforating tool, the upper end of the flowpassage being connected to a reservoir containing a compatibleperforating fluid and the lower end of the flow passage having a portbeneath the perforating tool opening into the annulus exterior to theperforating tool whereby the compatible perforating fluid may be pumpedinto the annulus at the lower extremity of the perforating gun todisplace the well fluids in the area to be perforated. In an alternativeembodiment, an external shield is placed around the perforating sectionhaving a lower outlet and a top inlet port in fluid communication withthe compatible perforating fluid whereby the perforating fluid entersthe annulus at the lower end of the perforating gun to displace the wellfluids in the area to be perforated.

These and other objects, features and advantages of the presentinvention will be more readily appreciated from a reading of thefollowing detailed specification and drawing, in which:

FIG. 1 is an elevated schematic view, partly in cross section,illustrating the earths subsurface having a borehole and having theapparatus of the present invention suspended therein and also showingthe surface electronics section which is used in conjunction with theapparatus according to the present invention;

FIG. 2 is an elevated view, partly in cross section, of the apparatusaccording to the present invention;

FIG. 3 is an elevated view, partly in cross section, of an alternativeembodiment of the apparatus according to the present invention; and

FIG. 4 is an expanded elevated view, partly in cross section, of aportion of the apparatus according to the present invention.

Referring now to the drawing in more detail for a more completedescription of the invention, in FIG. 1 is shown a well perforating tool10 suspended on an electrically conductive cable 11 in a well bore 12 inwhich well pipe string or casing 13 has been run and set. The conductivecable 11 extends to the earths surface and in a manner known to those inthe art is connected to the surface electronics section 14. Theinstrument 10 includes a plurality of shaped charges 15 or some othersuch well known perforating elements, for example, bullet perforators.The instrument 10 also carries a flexible rubber-like diaphragm member16 which restricts fluid movement to the area below the diaphragm aswill be more readily appreciated from the following description.lt-shouldbe appreciated that a conventional hoisting mechanism 17 at theearths surface in conjunction with the conductive cable 11 allows theinstrument 10 to traverse the borehole 12 until such. time as theperforating elements 15 are in the proper location to perforate the pipe13.

Referring now to FIG. 2, there is illustrated in greater detail theapparatus 10 according to the present invention. The top sub 20 of theinstrument 10 contains a DC motor illustrated in FIG. 4, coupled to arotary pump through an appropriate gear box. The rotary pump ispressure-balanced by drawing on well fluid for intake at the hydrostatichead existing at the point of operation. A floating piston 21 containedwithin the fluid reservoir 22 is arranged such that the rotary pump,within the top sub 20 transfers well fluid to the top side of thefloating piston 21. The reservoir 22 is filled with a compatibleperforating fluid which may be, for example, water with starch or CMC toreduce filtration or oil containing a soluble fluid loss additive orsome other such completion fluids such as those disclosed in US. Pat.No. 2,898,294 entitled WELL COMPLETION FLUIDS, or in US. Pat. No.2,894,584 entitled WELL COMPLETION, each of such patents being issued toG. G. Priest et al. It should be apprefciated that the reservoir 22 ispreferably sufficiently forating elements are connected in aconventional manner to the conductive cable 111 to enable the activationof such elements. um? W Referring now to FIG. 4, there is illustrated ingreater detail the top sub of the instrument 10. A conventional DC motor70, having electrical conductors 71 and 72 carried by the cable 11, isconnected through an appropriate gear box or other means to a rotarypump 73. The pump 73 has an inlet 74 in fluid communication with theport 75 and also has an outlet 76 in fluid communication with the fluidin the reservoir 22 above the piston 21 illustrated in FIG. 2.

In the operation of the apparatus according to FIG. 2, the pump withinthe upper sub 20 is activated by a DC voltage applied from the earthssurface along the conductive cable 11 to cause the piston 21 to movedown within the reservoir 22 and force the compatible perforating fluidfrom the reservoir 22' through the tube 23 and out through the outlet 24into the annulus at the lower end of the perforating section 25 and thenupward along the exterior of the perforating section 25 in the annulusbetween the instrument l0 and the casing 13. The outlet 24 includes aplurality of holes equally spaced to ensure that the incompatible wellfluid is swept cleanly from the annulus. As the incompatible well fluidis swept upwardly, it enters the reservoir 22 above the floating piston21 and is kept from going further up the borehole by the diaphragm 16.

It should be appreciated from the foregoing description of the apparatusof FIG. 2 and the operation thereof, that such an instrument offers vastsuperiority over the systems which have been built in accordance withthe prior art. By causing the compatible fluid to be pumped into theannulus at the bottom of the perforating section, there is no concernwith such intricate internal piping as is required with the prior artwherein it is necessary to maintain the compatible fluids separate fromthe incompatible well fluids. The simple operation of the apparatusaccording to FIG. 2 allows'the compatible fluid to be pumped out of thebottom of the apparatus and the incompatible well fluids to be displacedfrom around the perforating section 25 and merely be added to thereservoir above the floating piston 21.

Referring now to FIG. 3, there is illustrated an alternative embodimentof the present invention wherein an instrument is adapted to traversethe earth borehole by means of the electrical conductor 51 in a manneras described with respect to the apparatus of FIG. 2. The apparatus 30also includes a rubber diaphragm number 56 to restrict fluid movement tothe area below the diaphragm. The upper sub 60 of the apparatus 30includes a DC motor coupled to a rotary pump through an appropriate gearbox, for example, as is illustrated in FIG. 4. A concentric tube 64contains the necessary firing circuit for firing the perforators, forexample, shaped charges contained within the perforating section 65. Aswith the embodiment illustrated in FIG. 2, the floating piston 61 isadapted to move within the reservoir 62 and to force the compatibleperforating fluid in the reservoir 62 beneath the floating piston 61into the annulus in the area beneath the apparatus 30. The lower end ofthe reservoir 62 is closed by the sub 66. The sub diverts the compatiblefluid from the reservoir 62 through equally-spaced distribution ports tocompletely fill the annulus between the perforating section 65 and anencircling shield member 67. The shield member 67 completely surroundsthe perforating section 65 and has a lower outlet 68 through which thecompatible perforating fluid can enter the annulus at 7 the lower end ofthe instrument 62 and thus be pumped through the annulus between theshield 67 and the casing 53. The spacers 69 help to maintain theconcentricity of the shield 67 with respect to the perforator section65. The port 68 at the lower end of the shield 67 distributes thecompatible fluid throughout the annulus between the shield 67 and thecasing 53. The reservoir 62 contains an adequate amount of compatibleperforating fluid to cover the length of the perforator section 65.

In the operation of the apparatus according to FIG. 3, the rotary pumpwithin the upper sub is activated from the earths surface by a voltageapplied over the conductive cable 51. The compatible well fluid in thereservoir 62 beneath the floating piston 61 is pumped through theplurality of ports in the lower sub 66 and thus into the annulus betweenthe shield 67 and the perforator section 65. The continued pumpingaction causes the compatible fluid to be forced down through the lowerport 68 and thus into the annulus between the shield 67 and the casing53 and back up to the portion of the reservoir 62 above the floatingpiston 61. It should thus be appreciated that there has been describedwith respect to the embodiment of FIG. 3 an apparatus which enablescompatible perforating fluid to be released at the bottom of theperforating tool and which allows compatible perforating fluid to bebetween the perforating apparatus and the casing to be perforatedwithout resort to internal piping within the perforating gun and whichthus allows conventional perforating guns to be used. As soon as thecompatible perforating fluid has displaced the incompatible well borefluid, the perforator elements are activated by the firing circuitwithin the concentric tube 64 from the earths surface and theperforating section, for example, having a plurality of shaped charges,perforates through the expendable shield 67, the casing 53 and on intothe earth formations.

Thus there have been described and illustrated herein the preferredembodiments of the present invention which provide new and improvedmethod and apparatus for providing compatible perforating fluids be.-tween well perforators and the casing to be perforated. It should beappreciated, however, that those skilled in the art will be able tomodify these embodiments but that such modifications will fall withinthe scope of the present invention. For example, instead of having asingle reservoir divided by a floating piston, first and secondreservoirs can be used, thefirst for collecting the displaced well borefluid and the second for transporting the compatible fluid.

The embodiments of the invention is which an exclusive property orprivilege is claimed are defined as follows:

1 An apparatus for perforating casing in an earth borehole, comprising:

an elongated instrument adapted to traverse said borehole;

a reservoir within said instrument;

a piston within said reservoir dividing said reservoir into an uppersection and a lower section, said upper section having at least oneintake port for re-' ements therein, said perforating section having afluid channel along its length at least to the lower extremity of saidperforating elements, said fluid channel being in communication with thelower section of said reservoir and having at least one outlet port forreleasing fluid from said lower section of said reservoir into theannulus between said lower perforating elements and said casing; andmeans for activating said piston.

2. An apparatus for perforating casing in an earth borehole, comprising:

an elongated instrument adapted to traverse borehole;

a reservoir within said instrument;

apiston within said reservoir dividing said reservoir into an uppersection and a lower section, said upper section having at least oneintake port for receiving borehole fluids, and said lower section havingat least one outlet port for releasing any fluid in said lower section;

a cylindrical perforating section connected to the lower end of saidinstrument having a plurality of perforating elements therein;

a cylindrical, expendable shield encircling saidperforating section toform an annulus between said shield and said perforating section, saidlower section outlet port being in communication with said formedannulus, said shield having at least one outlet port at a location atleast to the lower extremity of said perforating elements for releasingfluid from said formed annulus into the annulus between said shield andsaid casing; and

means for activating said piston.

3. An apparatus for perforating casing in an earth borehole, comprising:

an elongated instrument adapted to traverse said borehole;

a reservoir within said instrument;

a piston within said reservoir dividing said reservoir into an uppersection and a lower section, said upper section having at least oneintake port for receiving borehole fluids;

said

a perforating section connected to the lower end of said instrumenthaving a plurality of perforating elements therein; and

means for releasing at least a portion of any fluid in said lowersection of said reservoir into the borehole at a point at least to thelower extremity of said perforating elements and to pump any boreholefluid displaced by said lower section fluid into said upper section ofsaid reservoir.

4. The apparatus according to claim 3 wherein said lower section of saidreservoir contains a compatible perforating fluid.

5. The apparatus according to claim 4 including in addition theretomeans carried by said instrument for preventing any substantial flow ofborehole fluid up past the upper section of said reservoir.

6. An apparatus for perforating casing in an earth borehole, comprising;

an elongated instrument adapted to traverse said borehole;

first and second fluid reservoirs within said instrument, said firstreservoir having at least an inlet port for receiving borehole fluids,and said second reservoir having at least one outlet port for releasingany fluid in said second reservoir;

a cylindrical perforating section connected to the lower end of saidinstrument having a plurality of perforating elements therein;

a cylindrical, expendable shield encircling said perforating section toform an annulus between said shield and said perforating section, saidsecond reservoir outlet port being in communication with said formedannulus, said shield having at least one outlet port at a location atleast to the lower extremity of said perforating elements for releasingfluid from said formed annulus into the annulus between said shield andsaid casing; and

means for causing any fluid in said second reservoir to be released outthrough said outlet port and to cause displaced well bore fluids to bepumped into said first reservoir.

are hereby corrected as shown below:

In the Heading:

After "INVENTOR:

( E Attest:

RUTH C. MASON Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATEOF QORRECTIUN PATENT NO. 3,856,094 DATED December 24, 1974 INVENTOR(S)Mike .Davis and Floyd 0. Bohn it is certified that error appears in theabove-identified patent and that sard Letters Patent both of-.

Signed and sealed this 15th day of July 1975.

C. MARSHALL DANN Commissioner of Patents and Trademarks

1. An apparatus for perforating casing in an earth borehole, comprising:an elongated instrument adapted to traverse said borehole; a reservoirwithin said instrument; a piston within said reservoir dividing saidreservoir into an upper section and a lower section, said upper sectionhaving at least one intake port for receiving borehole fluids; aperforating section connected to the lower end of said instrument havinga plurality of perforating elements therein, said perforating sectionhaving a fluid channel along its length at least to the lower extremityof said perforating elements, said fluid channel being in communicationwith the lower section of said reservoir and having at least one outletport for releasing fluid from said lower section of said reservoir intothe annulus between said lower perforating elements and said casing; andmeans for activating said piston.
 1. An apparatus for perforating casingin an earth borehole, comprising: an elongated instrument adapted totraverse said borehole; a reservoir within said instrument; a pistonwithin said reservoir dividing said reservoir into an upper section anda lower section, said upper section having at least one intake port forreceiving borehole fluids; a perforating section connected to the lowerend of said instrument having a plurality of perforating elementstherein, said perforating section having a fluid channel along itslength at least to the lower extremity of said perforating elements,said fluid channel being in communication with the lower section of saidreservoir and having at least one outlet port for releasing fluid fromsaid lower section of said reservoir into the annulus between said lowerperforating elements and said casing; and means for activating saidpiston.
 2. An apparatus for perforating casing in an earth borehole,comprising: an elongated instrument adapted to traverse said borehole; areservoir within said instrument; a piston within said reservoirdividing said reservoir into an upper section and a lower section, saidupper section Having at least one intake port for receiving boreholefluids, and said lower section having at least one outlet port forreleasing any fluid in said lower section; a cylindrical perforatingsection connected to the lower end of said instrument having a pluralityof perforating elements therein; a cylindrical, expendable shieldencircling said perforating section to form an annulus between saidshield and said perforating section, said lower section outlet portbeing in communication with said formed annulus, said shield having atleast one outlet port at a location at least to the lower extremity ofsaid perforating elements for releasing fluid from said formed annulusinto the annulus between said shield and said casing; and means foractivating said piston.
 4. The apparatus according to claim 3 whereinsaid lower section of said reservoir contains a compatible perforatingfluid.
 5. The apparatus according to claim 4 including in additionthereto means carried by said instrument for preventing any substantialflow of borehole fluid up past the upper section of said reservoir. 6.An apparatus for perforating casing in an earth borehole, comprising: anelongated instrument adapted to traverse said borehole; first and secondfluid reservoirs within said instrument, said first reservoir having atleast an inlet port for receiving borehole fluids, and said secondreservoir having at least one outlet port for releasing any fluid insaid second reservoir; a cylindrical perforating section connected tothe lower end of said instrument having a plurality of perforatingelements therein; a cylindrical, expendable shield encircling saidperforating section to form an annulus between said shield and saidperforating section, said second reservoir outlet port being incommunication with said formed annulus, said shield having at least oneoutlet port at a location at least to the lower extremity of saidperforating elements for releasing fluid from said formed annulus intothe annulus between said shield and said casing; and means for causingany fluid in said second reservoir to be released out through saidoutlet port and to cause displaced well bore fluids to be pumped intosaid first reservoir.